The Book of Staying in The Pit
Mentioned in Pyramids, this is a holy book in Djelibeybi about the god Yay
Annotation
Other mentioned books are things like "The Book of Going Forth", "The Book of Going Forth Around Elevenish" (which is attributed to a rather lazy Llamaic sect). These emphasize that the spiritual journey to enlightenment begins in the (metaphorical) morning, even if it is around elevenish.
In Britain, a demotic metaphor for "bed" is "pit". This book might therefore be to spiritual enlightenment what Rincewind is to heroism - an anti-text that advocates "sod enlightenment, have a long lie-in", which would be the ultimate extension of the logic of this escalating joke in Pyramids